It is known that in a vehicle including a stepped transmission mechanism, when friction engaging elements to which no engagement commands are outputted are engaged, interlock where brake force is generated and the vehicle is decelerated although a driver does not depress a brake pedal occurs.
JP2008-232355 discloses a control device which detects occurrence of interlock where friction engaging elements to which no engagement commands are outputted are brought into an engaged state on the basis of deceleration of a vehicle, a command gear position to a stepped transmission mechanism, and an actual gear ratio which is a ratio of rotation speed of input and output shafts of the stepped transmission mechanism.